Observations of earth's bow shock for low mach numbers

Four anomalous Earth's bow shock locations observed during 1969 are studied, using plasma and magnetic field data of the European satellite HEOS-1. It results that when no magnetic storms are present, the shock position is predicted with a good approximation by magneto-hydrodynamic equations, making use of the magnetosonic Mach number of the solar wind. When magnetic storms are present, symmetric and asymmetric ring currents should be taken into account. For low magnetosonic Mach numbers (1<MMS < 3), the magnetosheath magnetic field is characterized by the unusual absence of low frequency turbulence. This experimental result seems to indicate that in such conditions the bow shock is a laminar shock.